Below is a list of FTP commands that may be sent to an FTP server, including all commands that are standardized in RFC 959 by the IETF. All commands below are RFC 959 based unless stated otherwise. Note that most command-line FTP clients present their own set of commands to users. For example, GET is the common user command to download a file instead of the raw command RETR.

On which account do you experience this problem? I checked your accounts, and the oldest one has hit the inode limit. If you hit the inode limit, you will not be able to create or update any more files, which would explain why the STOR command would fail.